This patch moved the remaining RPC calls away from the
MDNS service to the Worker and re-worked them to better
match the patterns used in the Worker. This means that
the MDNS service now only handles incoming DNS queries.
In addition the metrics backend has been removed as it was
only used by the MDNS RPC implementation and the monascastatsd
implementation no longer serves a purpose.
Closes-Bug: #1978742
Closes-Bug: #1978743
Change-Id: I5ef106717546a201fd62a51adacd43495c148cd4